1. Technical Field
The present invention relates to flip-chip technologies, and more specifically, to soft error issue in flip-chip technologies.
2. Related Art
In flip-chip technologies, solder bumps are typically formed on top of a semiconductor chip (i.e., integrated circuit IC). Each solder bump is formed directly on a bond pad of the chip. The chip is then flipped face down and then aligned to a package/substrate so that the solder bumps are bonded directly, simultaneously, and one-to-one to the pads of the package/substrate (called package/substrate pads). After that, an adhesive underfill material is used to fill the empty space between the chip and the package/substrate. Once in place, the adhesive underfill material is cured at a high temperature so as to form a solid underfill layer that tightly bonds the chip to the package/substrate. In some applications, multiple chips can be attached (i.e., bonded) to a single substrate using flip-chip technologies so as to form a multi-chip module (MCM). However, if one of the chips in the MCM is later found defective through testing, the entire MCM is wasted because with current materials it is not possible to replace the defective chip of the MCM (because all the chips of the MCM are tightly bonded to the substrate by the solid underfill layer). One way to solve this problem is to forgo the solid underfill layer by omitting the underfill process. However, for ceramic substrates, without the solid underfill layer separating the substrate from the chips, alpha particles (large subatomic fragments consisting of 2 protons and 2 neutrons) that continuously emit from the substrate would easily enter the chips of the MCM resulting in a substantially larger number of soft errors in the MCM during the normal operation of the MCM.
Therefore, there is a need for a structure (and a method for forming the same) that allows omission of underfill for chip replacement without substantially increasing the soft error rate in the structure during the normal operation of the structure.